1. Technical Field
The present disclosure relates generally to microwave applicators used in tissue ablation procedures. More particularly, the present disclosure is directed to a modified version of a choked wet-tip ablation antenna.
2. Background of Related Art
Treatment of certain diseases requires destruction of malignant tissue growths (e.g., tumors). It is known that tumor cells denature at elevated temperatures that are slightly lower than temperatures injurious to surrounding healthy cells. Therefore, known treatment methods, such as hyperthermia therapy, heat tumor cells to temperatures above 41° C., while maintaining adjacent healthy cells at lower temperatures to avoid irreversible cell damage. Such methods involve applying electromagnetic radiation to heat tissue and include ablation and coagulation of tissue. In particular, microwave energy is used to coagulate and/or ablate tissue to denature or kill the cancerous cells.
Microwave energy is applied via microwave ablation antennas that penetrate tissue to reach tumors. There are several types of microwave antennas, such as monopole and dipole. In monopole and dipole antennas, microwave energy radiates perpendicularly from the axis of the conductor. A monopole antenna includes a single, elongated microwave conductor. Dipole antennas typically have a coaxial construction including an inner conductor and an outer conductor separated by a dielectric portion. More specifically, dipole microwave antennas include a long, thin inner conductor that extends along a longitudinal axis of the antenna and is surrounded by an outer conductor. In certain variations, a portion or portions of the outer conductor may be selectively removed to provide for more effective outward radiation of energy. This type of microwave antenna construction is typically referred to as a “leaky waveguide” or “leaky coaxial” antenna.
A typical tissue-penetrating (i.e., percutaneously inserted) microwave energy delivery device includes a transmission portion formed by a long, thin inner conductor that extends along the axis of the device. The inner conductor is surrounded by a dielectric material and the outer conductor is radially-disposed relative to the dielectric material and forms a coaxial waveguide for transmitting a microwave signal. The distal end of the transmission portion of the outer conductor connects to a microwave antenna configured to receive the microwave signal from the transmission portion and to radiate the microwave energy signal to tissue.
Structural strength is provided to the microwave energy delivery device by surrounding at least part of the transmission portion and/or the microwave antenna with a high-strength jacket. The distal end of the high-strength jacket may connect to, or form, a sharpened tip for piercing tissue.
Invasive procedures have been developed in which the microwave antenna delivery device is inserted directly into a point of treatment via percutaneous insertion. Such invasive procedures potentially provide better temperature control of the tissue being treated. Because of the small difference between the temperature required for denaturing malignant cells and the temperature injurious to healthy cells, a known heating pattern and predictable temperature control is important so that heating is confined to the tissue to be treated. For instance, hyperthermia treatment at the threshold temperature of about 41.5° C. generally has little effect on most malignant growths of cells. However, at slightly elevated temperatures above the approximate range of 43° C. to 45° C., thermal damage to most types of normal cells is routinely observed; accordingly, great care must be taken not to exceed these temperatures in healthy tissue.
Systems and methods developed to control heating and prevent elevated temperatures to surrounding tissue typically include cooling fluid that circulates around at least a portion of the microwave energy delivery device. For example, in one system cooling fluid is provided to the distal end of the microwave energy delivery device via a thin-walled tube. The thin-walled tube deposits the cooling fluid near the microwave antenna and the cooling fluid flows proximally through a return path in the microwave energy deliver device.
There are several challenges to providing cooling to a microwave energy delivery device. The first challenge is providing suitable supply and return fluid pathways in the microwave energy delivery device without increasing the overall diameter of the microwave energy delivery device. Another challenge is providing suitable supply and return fluid pathways while maintaining a concentric configuration throughout the microwave energy delivery device. Yet another challenge is providing a suitable configuration that simplifies assembly and manufacturing.